Thin-wall stainless steel pipes have been widely used inside or outside buildings for conducting a fluid such as water or steam. These thin-wall stainless steel pipes are replacing iron and copper pipes which are liable to corrosion, causing leakage, and vinyl pipes which have low resistance against both heat and cold weather.
Because stainless steel is very expensive and very hard but very extendible and malleable, the wall thickness of a stainless steel pipe is usually made approximately one millimeter. Consequently, it is difficult to thread the end portions of these thin-wall stainless steel pipes and join them with a nut. For this reason, soldering, welding, and double folding interlock have been used to connect them.
However, these joints do not have satisfactory strength against pulling force, are not removable and liable to corrosion, and require a skilled worker for making such connection. Thus, the inventor of this application has proposed a new joint mechanism in the Japanese U.M. Patent Application No. 58-2005 (Japanese U.M. Patent Application Kokai No. 59=107390). This joint mechanism includes a V-shaped annular bead with a pair of inclined bearing faces on an end portion of a thin-wall stainless steel pipe and a joint sleeve having a diameter sufficiently large to receive the pipe. A male thread and an annular recess are provided on the outside surface and the inside edge of the joint sleeve, respectively. The joint sleeve is fitted over the pipe such that it abuts on a inclined face of the annular bead via an annular seal which is set in the annular recess. A coupling nut having an inside edge tapered so as to abut on the other inclined face of the annular bead is threaded over the joint sleeve to connect the pipe to the joint sleeve.
However, it has been impossible to check accurately by observation whether or not the coupling nut is completely tightened to the joint sleeve. As a result, the installer has had to guess when the coupling nut is tightened completely by feeling the resistance to further tightening, counting the number of turns of the coupling nut, or measuring the distance between the joint sleeve and the coupling nut. These operations, however, are not only troublesome but also inaccurate.
Accordingly, it is an object of the invention to provide a joint mechanism for thin-wall stainless steel pipes, which is able to withstand a large pulling force and easy to disconnect or remove, does not require a skilled worker, and enables anyone to observe the exact tightness of a coupling nut.